Diluting liquid samples

ABSTRACT

The diluter disclosed herein consists of a control and drive unit and a diluent module which is connectable to the control and drive unit to form a diluter apparatus. In the diluent module, which can be removed and replaced for the rapid and non-contaminating substitution of diluents, a diluent piston engages the walls of a cylindrical diluent reservoir which has an outlet at one end. A bore through the diluent piston receives and supports a second, smaller piston which can be moved independently of the diluent piston. With appropriate connections to the drive unit, the small piston may be moved in a direction away from the diluent outlet, thereby aspirating a small sample of liquid placed in contact with a spout which communicates with the diluent outlet. Subsequent movement of the diluent piston toward the outlet enables the dispensing from the spout of the relatively small sample of liquid along with a relatively large quantity of diluent. The drive unit includes separate, preferably coaxial, drive rods having engagement portions for releasable connection to the pistons of the diluent module. A stepping motor drives the diluent piston and a motor control unit includes selector means permitting the selection of the precise number of incremental rotations of the stepping motor&#39;s rotor, thereby enabling selection of the precise quantity of diluent to be dispensed when the diluent piston is driven toward the outlet.

BACKGROUND OF THE INVENTION

This invention relates to an automatic diluter and more particularly toa diluter which permits aspiration of a very small sample and subsequentdilution of the sample at very high ratios.

Automatic diluters are available which provide for the aspiration of apredetermined quantity of a sample fluid, followed by the discharge ofthe measured sample together with a predetermined quantity of diluent.While there are many particular constructions of diluters of this class,in each the change of diluent involves the flushing of various hydrauliclines and connections in order to prevent diluent contamination by apreviously used diluent. Such diluters typically require a valveassembly for switching purposes between aspirate and dispense modes ofoperation, the valve assembly being a relatively expensive sub-assemblyof the diluter and being a source of possible error.

Another type of apparatus provides a self-contained diluent unit whichis removable from the dispenser for subsitution by another diluent unitcontaining a different type of diluent. A dispensing piston within thediluent unit is driven to dispense diluent through an outlet fordiluting a liquid sample which has been measured using other apparatus.The operation of this class of apparatus, therefore, is less useful thanan automatic diluter capable of both measuring the sample and dispensingthe diluent.

Among the objects of the present invention may be noted the provision ofan automatic diluter, and of a diluent module incorporated therein,which facilitates the automatic aspiration of a relatively small sampleof liquid and the dilution of that sample with a relatively large volumeof diluent, wherein the diluent module is removable from the remainderof the diluter and is interchangeable with other such modules.

Further objects include the provision of an automatic diluter whicheliminates hydraulic lines and valving, which permits recovery of unuseddiluent, and which permits a convenient and precise selection of a widevariety of dilution ratios.

SUMMARY OF THE INVENTION

Briefly, a diluter in accordance with the present invention comprises adiluent cylinder having an outlet and a conduit communicating with thatoutlet. A diluent dispensing piston within the cylinder is driven byfirst drive means capable of moving the diluent piston toward thecylinder outlet in order to force the diluent from the cylinder, throughthe outlet, and into the conduit. A second piston, of relatively smallercross section than the diluent piston, is supported in a bore in thediluent piston and is movable with respect to the diluent piston. Asecond drive means is capable of moving the second piston independentlyof the diluent piston for a relatively short distance in a directionaway from the cylinder outlet. Thus, movement of the second, smallerpiston enables aspiration into the conduit of a relatively small sampleof a liquid and subsequent movement of the diluent piston toward theoutlet enables ejection from the conduit of that small sample along witha relatively large quantity of diluent.

Preferably, the apparatus comprises a control and drive unit and aseparable diluent module. The drive unit includes a first drive rodreleasably engagable with the diluent piston and a second drive rodreleasably engagable with the second piston. The first drive rod isdriven by a stepping motor controlled by a motor control unit whichincludes a counter for counting a predetermined number of clock pulsesand for causing an incremental rotation of the stepping motor for eachpulse up to the predetermined number. The motor control unit furtherincludes means for selecting the total number of pulses countable, thusfacilitating adjustment of the stroke of the diluent piston and,consequently, the quantity of diluent dispensed by the apparatus.

Other objects, features, and advantages of the invention will be in partapparent and in part pointed out hereinafter in connection with thedescription of an illustrative embodiment shown in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation of a diluter constructed in accordance withthe present invention;

FIG. 2 is a view taken at 2--2 of FIG. 1;

FIGS. 3A and 3B are enlarged sectional views of the releasableconnection of the sampling piston and its drive rod; and

FIG. 4 is a logic diagram of the control and drive unit of the diluterof FIGS. 1 and 2.

DETAILED DESCRIPTION OF A PARTICULAR PREFERRED EMBODIMENT

Referring first to FIG. 1, there is shown a diluter consisting of acontrol and drive unit 11 and a diluent module 13 secured to ahorizontal surface 15 of the unit 11 by a retainer clip 17. Controls 19,21, 23, 25, 27, and 29 and an indicator 31 are mounted on the frontfaces 33 and 35 of the unit 11 and have functions discussed below inconnection with FIGS. 2 and 4.

Referring now to FIG. 2, the diluent module 13 comprises a cylinder 37,which acts as a diluent reservoir, and a cap assembly 39 secured to oneend of the cylinder 37 and defining an outlet 41. An internal conduit 43in the cap assembly 39 connects the outlet 41 with a probe or spout 45which tapers to a generally downwardly directed outlet 47 of its own. Adiluent dispensing piston 49 is provided within the cylinder 37 andengages the internal walls of the cylinder. A resilient sealing member51 in an external groove in the piston 49 assists in maintaining aleak-proof fit of the piston 49 with the wall of cylinder 37. A centralbore 53 in the piston 49 receives a second, smaller piston 55 which isslidable within the bore 53. A resilient sealing member 57 is providedin a circular recess in the surface of the bore 53 to seal against thesurface of piston 55. The piston 55 has a length at least as long as thelength of cylinder 37, thereby enabling a beveled end surface 59 thereofto engage a matching bevel of the outlet 41, while the opposite end 61of the piston 55 remains within bore 53 below the seal member 57. Aflange 63 at the end of cylinder 37 opposite the cap assembly 39 issized to be received in a recess 65 in the horizontal surface 15 of thecontrol and drive unit and to be engaged by the retainer clip 17 forsecuring the diluent module 13 to the unit 11.

Still referring to FIG. 2, a bearing member 67, mounted in a circularopening in horizontal surface 15 which is centered in recess 65, servesas a guide, and a stop, for a first, hollow, vertically disposed driverod 69. A coupling chuck at the upper end of drive rod 69 projects abovethe recess 65 owing to a shoulder 71 of the drive rod which engages theupper surface of bearing member 67, thereby defining a stop in thedownward motion of the drive rod. The coupling chuck consists of aportion 73 of the drive rod 69 having a reduced wall thickness, therebyfacilitating radial flexibility at that point, and an inwardly facingannular lip 75, adjacent the portion 73, engagable with a mating,externally facing, annular lip 77 of the piston 49. A verticallydisposed gear rack 79 is recessed in the external surface of drive rod69 and engages a pinion gear 81 secured to the rotary member (not shown)of a stepping motor 83 which is supported within the unit 11 by abracket 85. Electrical leads 87 extend between the motor 83 and acircuit board 89 supported within the unit 11.

A second drive rod 91 is coaxial with, and extends through the hollowinterior of, drive rod 69. The second drive rod 91 extends downwardlybelow the lower end of the first drive rod 69 and fits into a hollowstud 93 projecting upwardly from the floor 95 of the drive unit 11. Acompression spring 97 within the stud 93 biases the second drive rod 91upwardly. A threaded cap 99, having an opening for receiving the driverod 91, engages mating threads on the exterior of stud 93 to provide anadjustable stop which limits the downward motion of the drive rod 91when a radial flange 101, integral with the drive rod 91, strikes theupper surface of the cap 99. A cam lever 103 is pivotally secured by pin105 to a structural member 107 projecting upwardly from the floor 95 ofthe unit 11 and bears against the flange 101 for driving the drive rod91 downwardly against the upward biasing force of the spring 97. The camlever 103 is driven by a solenoid coil 109, also secured to the member107, having an armature 111 coupled through a clevis spring 113 to amember 115 having a pin 117 disposed within a slot 119 of the cam lever103. This arrangement causes cam lever 103 to pivot about pin 105 inresponse to the linear movement of armature 111. Leads 121 extend fromthe solenoid coil 109 to the circuit board 89.

Also engagable with flange 101 is an eccentric wheel 123 mounted on ashaft 125 which is supported for rotation in a member 127 projectingupwardly from the floor 95 adjacent the flange 101 and a bushing 129mounted in the front face 33 of unit 11. The control knob 19 is securedto the shaft 125 for rotation therewith. Rotation of the control knob 19causes the eccentric wheel 123 to rotate thereby camming the flange 101,and the drive rod 91, downwardly a short distance against the force ofbiasing spring 97. As discussed in detail below, when the drive rod 91is engages with the piston 55 of the diluent module 13, this movementcauses the beveled upper surface 59 of the piston 55 to disengage fromthe outlet 41 of the diluent cylinder 37.

The coupling of the upper end of the second drive rod 91 with the lowerend of piston 55 will be best understood by reference to FIGS. 3A and3B. An axial bore 131 is provided in the lower end of piston 55, as isan annular radial groove 133 in the internal surface of the bore 131. Abore 135 is also provided in the upper end of piston 91 and a plunger137, upwardly biased by plunger spring 139, is disposed within the bore135. A transverse bore 141 in the piston 91 intersects the bore 135adjacent the head 143 of the plunger 137. An eccentric latch pellet 145is disposed for transverse sliding motion in the bore 141. As best seenin FIG. 3B, the upward force of plunger 137 biases the latch pellet 145to an orientation in which a hemispherical lobe 147 protrudes beyond theouter surface of the piston 91. In that orientation, the lobe 147 mayengage the groove 133 thereby connecting the drive rod 91 to the piston55. The insertion of the drive rod 91 into the bore 131 displaces thehemispherical lobe 147 against the influence of the plunger biasingspring 139 (see FIG. 3A). By choosing the spring 97, at a lower end ofthe drive rod 91, to have a substantially greater compressive force thanthe plunger spring 139, the drive rod 91 will not move downwardly as thesurface of bore 131 bears upon the latch pellet 145 causing a downwardforce against spring 139 to be transmitted to the drive rod 91.

FIG. 4 is a logic diagram of the circuitry incorporated in the controland drive unit 11. The drive motor 83 has a pair of center-tapped drivewindings 151 and 153 for producing rotation in the forward and reversedirections respectively. The opposite ends of these windings are driven,through respective J-K flip-flop circuits 158 and 159. A clock oscilator149 provides a continuous pulse train output signal. This signal isapplied directly to the clock input of flip-flop 158 and, through a NANDgate 160, to the clock input of flip-flop 159. Passage of the clockpulses through the gate 160 is controlled by an R-S flip-flop 161comprising a pair of NAND gates 163 and 164.

For generating a pulse string of predetermined length, the controlapparatus of FIG. 4 employs a preset counter comprising three BCD decadecounters 165-167, together with respective decade selection switches165a-167a which together make up the diluent volume selection switch 29.Clock pulses passed by the gate 160 are applied to the string ofcounters 165-167 as well as to the motore drive circuitry. When eachdecade counter reaches the value determined by the setting of therespective switch 165a-167a, an output signal is passed by the switch.These three output signals are combined in a NAND gate 169 to generate asignal which resets the flip-flop 161 when there is an overall matchbetween the value held in the counter and the setting of the switch 29.

The flip-flop 161 may be placed in its set state to initiate a dispensecycle by pressing the push-button switch 23 which is interconnected withthe NAND gate 164 as shown. The operation of the switch 23 also resetsthe counters 165-167, the counters being released to commence countingwhen the button is released. Accordingly, each time the push-buttonswitch 23 is momentarily operated, a pulse string is initiated whichcontinues until the number of pulses counted equals the value set intothe switches 165a-167a.

The drive motor 83 may be continuously energized in the forwarddirection by depressing the push-button switch 27 which opens the gate160 independently of the state of the flip-flop 161. Continuousoperation of the drive motor 83 in the reverse direction is obtained bydepressing the push-button switch 25 which is interconnected with the Jand K inputs of the flip-flop 158 so that, when the button is operated,the flip-flop will respond to clock input pulses and energize thereverse winding 153. As will be understood by those skilled in the art,the J-K flip-flop 158 is otherwise unresponsive to the clock signalcontinuously applied thereto. The solenoid 109 is controlled through adriver amplifier 171, by a J-K flip-flop 173. The solenoid may beenergized by depressing the push-button switch 21 which isinterconnected with the J input of the flip-flop. When push-buttonswitch 21 is released, the solenoid will remain energized in the absenceof any pulse signals applied to the clock input of the flip-flop. Suchclock pulses are applied, through NAND gate 175, only when the motor isagain energized. Accordingly, when the solenoid is energized to aspiratea sample, the sample will not be immediately ejected when the control 21is released but rather is ejected together with the diluent.

In the operation of the apparatus as described above, a diluent module13, having its cylinder 37 filled with the module vertically into therecess 65 in the surface 15 of the unit 11 and applying the necessarydownward pressure to cause the radial flexing of the reduced thicknessportion 73 of drive rod 69 and additionally, the displacement of latchpellet 145 with the attendent compression of plunger spring 139. Thismanual downward pressure causes the engagement of each of the drive rodswith the respective pistons 49 and 55. With the cylinder flange 63seated in the recess 65, the retainer clip 17 is pressed into place tosecurely retain the module 13 on the unit 11.

Prior to use of the module 13, the beveled upper surface 59 of thesample aspirating piston 55 engages the outlet 41 to form a valveblocking the outlet, thereby preventing leakage of diluent through theoutlet 41, conduit 43, and spout 45 during the shipping or storage ofthe module 13. Prior to the diluting sequence of operation of theapparatus, this valve is opened by merely rotating the control knob 19to cause the eccentric wheel 123 to depress drive rod 91 and theattached piston 55 a small amount, thereby opening the outlet 41 ofcylinder 37. With a container in place beneath the outlet 47 of spout45, the conduit 43 and spout 45 are filled with diluent by momentarilydepressing the ready control 27 which is connected, as will be clear tothose skilled in the art from the schematic diagram of FIG. 4, tooperate the stepping motor 83 and thus drive the diluent piston 49.

With the conduit 43 and spout 45 filled with diluent, the outlet 47 ofspout 45 is submerged in a container of the sample fluid and the sampleaspirate control 21 is pressed. This control energizes the solenoid 109and thereby causes the downward stroke of piston 55 for a distancedetermined by the position of the stop 99. This causes the aspirationinto the spout 45 of a volume of sample fluid equal to the volume ofpiston 55 withdrawn from the cylinder. Because of the small diameter ofpiston 55 and the small downward stroke permitted by the stop 99, a verysmall volume of sample can be aspirated into spout 45. The volumeaspirated can be precisely determined by adjusting the stroke of thepiston 55 using the adjustable stop 99.

Next, a container for the diluted sample is placed beneath the outlet 47of probe 45 and the dispense control 23 is pressed. As described withreference to FIG. 4, this control causes the operation of motor 83 forpredetermined number of incremental rotations, the number being equal tothat set by the diluent quantity selection switch 29. The displacementof the piston 49 for each incremental rotation of the rotary member ofthe motor 83 can be determined for any given motor and gearingarrangement. Accordingly, by a suitable choice of the dimensions ofpiston 49 and cylinder 37 in relation to the gearing, the control 31 canbe made to read directly in milliliters. The arrangement described,therefore, permits the convenient and precise selection of the desiredvolume of diluent to be dispensed by the apparatus.

When the diluent has been dispensed, the module 13 may be removed andanother installed in the manner described above. Alternatively, theempty module 12 may be refilled by submerging the outlet 47 of the probe45 in a container of diluent and depressing the piston return control 25which causes the piston 49 to be driven downwardly by the reverserotation of the motor's rotary member. This motion of the piston 49aspirates diluent from the container into the cylinder 37.

In view of the foregoing, it may be seen that the several objects of thepresent invention are achieved and other advantageous results have beenattained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it should be understood thatall matter contained in the above description, or shown in theaccompanying drawings, shall be interpreted as illustrative and not in alimiting sense.

1. Apparatus for diluting a sample of liquid with a diluent comprisingadiluent cylinder having an outlet at one end thereof, a conduitcommunicating with said cylinder outlet, a diluent dispensing pistonwithin said cylinder of substantially the same cross section as saidcylinder and having a bore therethrough, and a second piston ofrelatively smaller cross section than said diluent dispensing pistonsupported in said bore for movement with respect to said diluentdispensing piston, piston drive means comprising first means for movingsaid diluent dispensing piston toward said cylinder outlet substantiallythe full length of said cylinder to dispense a large fraction of diluentcontained in said cylinder, and second means for moving said secondpiston relative to said diluent dispensing piston in a direction awayfrom said cylinder outlet for a distance much less than the full lengthof said cylinder; whereby movement of said second, smaller pistonenables aspiration of relatively small sample of liquid into saidconduit and subsequent movement of said diluent dispensing piston towardsaid outlet enables ejection from said conduit of said relatively smallsample along with a
 2. The apparatus of claim 1 wherein said first andsecond pistons are
 3. The apparatus of claim 2 wherein said cylinderoutlet is coaxial with said second piston, thereby enabling said secondpiston to block said cylinder outlet, to prevent premature delivery ofdiluent to said conduit, prior to said movement of said second pistonaway from said cylinder
 4. The apparatus of claim 1 wherein said firstpiston has a cross section
 5. The apparatus of claim 1 wherein saidfirst means for moving said first piston comprise a stepping motorhaving an incrementably rotatable rotary member connected to linearlydrive said first piston and motor control means for causing apredetermined number of incremental rotations of said
 6. The apparatusof claim 5 wherein said motor control means further comprise means forselecting said predetermined number of incremental rotations, therebyselecting the stroke of said first piston and the
 7. A diluent modulefor use with a drive means to provide an apparatus for diluting a sampleof liquid with a diluent, the diluent module comprisinga cylinder forholding diluent, an outlet at one end of said cylinder, a dispensingspout, a conduit interconnecting said outlet and said dispensing spout,a first piston within said cylinder engaging the walls thereof in asubstantially leak-proof engagement, said first piston having a surfacewith a bore therethrough facing said outlet and a reverse surface forreceiving driving force from said drive means to move said first pistontoward said outlet, and a second piston of smaller cross section thansaid first piston supported in leak-proof engagement in said bore formovement relative to said first piston, said second piston having asurface facing said outlet and a reverse surface having coupling meansfor engagement with said drive means thereby enabling movement of saidsecond piston in direction away from said outlet; whereby movement ofsaid second, smaller piston in a direction away from said outlet enablesaspiration of a relatively small sample of liquid into said spout andsubsequent movement of said first, larger piston toward said outletenables the dispensing from said spout of said relatively small sampleof liquid along with a relatively large quantity of diluent.
 8. Thediluent module of claim 7 wherein said first piston has a cross sectionof at least about ten times the cross section of said second
 9. Thediluent module of claim 7 wherein said cylinder outlet is coaxial withsaid second piston, thereby enabling said second piston to block saidcylinder outlet, to prevent premature delivery of diluent to saidconduit, prior to said movement of said second piston away from saidcylinder
 10. The diluent module of claim 9 wherein said outlet isbevelled and said first piston surface that faces outlet has a matchingbevel, thereby
 11. The diluent module of claim 7 wherein said couplingmeans comprise a detent in an internal bore in said reverse surface ofsaid second piston, said detent disposed to receive a bead on a driverod of said drive means
 12. Apparatus for diluting a sample of liquidwith a diluent comprising a drive unit and diluent module releasablyconnectable to said drive unit,said diluent module comprising a diluentcylinder having means engagable with said drive unit for releasablyconnecting said diluent module to said drive unit, an outlet at one endof said cylinder, a dispensing spout, a conduit interconnecting saidoutlet and said dispensing spout, a first piston within said cylindercoaxial therewith and engaging the walls thereof in a substantiallyleak-proof engagement, said first piston having a surface facing saidoutlet and a reverse surface which includes coupling means for receivingdriving force from said drive unit to move said first piston toward saidoutlet, and a second piston within said cylinder, said second piston ofsmaller cross section that said first piston and having a surfaceaccessible from the exterior of said diluent module, said surface havingcoupling means for engagement with said drive unit thereby enablingmovement of said second piston in direction toward its coupling means;said drive unit comprising a first drive rod releasably connectable tosaid first piston coupling means, a motor for driving said first driverod toward said first piston for moving said first piston toward saidoutlet, a second drive rod releasably connectable to said second pistoncoupling means, means for driving said second drive rod for apredetermined distance in a direction so as to withdraw at least aportion of said second piston from said cylinder, and valve means forselectively blocking the flow of diluent from said cylinder
 13. Theapparatus of claim 12 wherein said first piston has a bore therethroughparallel to the axis of said cylinder, said second piston beingsupported in said bore for movement with respect to said first
 14. Theapparatus of claim 13 wherein said second piston and said outlet arecoaxial, said valve means comprising a surface of said second pistonengagable with the interior surface of said cylinder around theperiphery
 15. The apparatus of claim 13 wherein said first and secondpistons are coaxial, said first drive rod being hollow and said seconddrive rod
 16. The apparatus of claim 12 wherein said first piston has across section
 17. The apparatus of claim 12 wherein said motor is astepping motor having an incrementally rotatably rotary member connectedto linearly drive said first piston, said apparatus further includingmotor control means for causing a predetermined number of incrementalrotations of said rotary
 18. The apparatus of claim 17 wherein saidmotor control means comprise means for selecting said predeterminednumber of incremental rotations, thereby selecting the stroke of saidfirst piston and the quantity of
 19. The apparatus of claim 18 whereinsaid motor control means comprise means for generating a continuoustrain of clock pulses, counter means for counting a predetermined numberof clock pulses, logic circuitry for driving said rotary member oneincremental rotation for each clock pulse thus counted, and means forselecting the maximum number of clock pulses countable by said countingmeans; whereby said last mentioned means enable selection of the desirednumber of incremental rotations of said rotary member, thereby selectingthe stroke of said first piston and the quantity
 20. Sample dilutingapparatus comprising:first piston means for aspirating a sample intosaid apparatus; electromechanical means which, when energized, movessaid first piston means to aspirate a sample; second piston means fordispensing diluent from said apparatus; stepping motor means foradvancing said second piston means to dispense diluent; a clock signalsource; multi-decade switch means settable to a preselectable value; amulti-decade digital counter means; gate means for selectively applyingsaid clock signal to said counter means and to said stepping motor foradvancing said diluent piston; a first flip-flop which, when set,effects energization of said electromechanical means; a second flip-flopwhich, when set, controls said gate means to energize said steppingmotor; circuit means for resetting said first flip-flop when saidstepping motor is energized; and control circuit means interconnectedwith said counter means and said switch means for resetting said secondflip-flop when the count value equals said preselected value, whereby,after the aspiration of a sample, a preselectable quantity of diluent isdispensed with the sample.